To protect the engine injection system, fuel filter systems are usually designed in such that not just impurities such as floating particulates, dust, etc., are separated, but also that water is separated and removed. Since the separated water may still be contaminated with diesel oil, it cannot be released directly into the environment. Specifically, the water may contain dissolved diesel components or micro-droplets that have not been separated by the pressure differential between the water and the diesel oil in the sump collected in the collection chamber. Consequently, prior art includes providing measures for purifying the separated water before it is released into the environment.
In this context, a fuel filter system of the type mentioned above is known from EP 1 581 736 B1. This known solution specifies that separated water that is still loaded with substances that are harmful to the environment are not to be released into the environment directly in the fluid phase. Rather, those substances are to be fed to an evaporation device from which the exhaust vapor is released into the environment downstream from the release device.
A generically different solution, cf. EP 1 726 818 A2, the separated water, without an evaporation or vaporization process taking place, is released into the environment in the fluid phase. Before release, a membrane permeable to water molecules, in the form of, for example, a ceramic membrane, retains the substances that are harmful to the environment. Aside from the fact that such membranes have to be replaced after a limited service life, they require that pressure be built up for flow pass-through to take place.